On the rare occasions that stay-at-home moms draw attention from the media, journalists tend to focus on “opt-out mothers”—married women with elite educations and prestigious jobs who choose to leave the workforce after having kids. But as a new report from Pew Research Center shows, they’re a small minority of moms who don’t work outside the house.

A total of 29% of mothers with children under 18 are stay-at-home moms (or SAHMs, in the common abbreviation). That number represents a small rise from a 1999 low of 23%, a proportion reached after a multi-decade fall from 47% in 1970. Only two-thirds of stay-at-home mothers are “traditional”: married with husbands who work. The other third of SAHMs are single (20%, down from a 1993 high of 29%), cohabiting (5%), or married with non-working husbands (7%).

Traditional SAHMs are the most likely to have truly opted out of working: 85% say that caring for children is the reason they’re not employed. Just 41% of their single counterparts say the same; they’re more likely to forgo paid work due to illness, disability, inability to find a job, or enrollment in school. Unsurprisingly, mothers who do not work outside the home are more likely to be poor (34%) than those who do (12%), and single, non-working mothers are especially likely to live in poverty (71%).

As the Pew researchers point out, women’s education levels and earning potential seem to shape their work decisions. Almost four in five mothers with college degrees work outside the home, compared to just 49% of women who lack a high school diploma (with mothers between the two educational extremes falling in between). Less-educated women may find that the only jobs available to them would hardly cover the cost of childcare, whereas for educated women, not working means sacrificing a significant amount of household income.

Of course, children’s ages also shape women’s work decisions: 51% of stay-at-home mothers have at least one child under age six, vs. 41% of working mothers. According to time use surveys, traditional SAHMs who have children under age six spend roughly twice as much time on child care as those whose children are all at least six years old.

Work decisions also vary by race and ethnicity: Nearly three-quarters of white and black mothers work outside the home, but just 62% of Hispanic mothers and 64% of Asian mothers. The Pew report attributes this fact to immigration status: 86% of Asian mothers and 60% of Hispanic ones were born outside the U.S., and immigrant mothers are 14 percentage points more likely to stay at home than U.S.-born ones (40% vs. 26%). (Immigrants are also considerably more likely than native-born Americans to be married.)

Regardless of whether they work or stay at home, many mothers desire a different situation: According to a different Pew report, 11% of working mothers would prefer not to work at all, and 50% would prefer part-time work. Thirty-six percent of non-working mothers say not working is their ideal situation, but 22% would like full-time work and 41% would like to work part-time.

At the same time, about half of working mothersand working fathers say that they work because they need the income, when they’d prefer to be home with their children. It’s hard to make sense of these figures without suspecting that the “grass is greener” adage is relevant here. All the same, these seemingly inevitable conflicts between parents’ desires and their current situations make policies geared toward flexibility all the more desirable.